fix: close marketplace client review findings

src/lib/host-api.ts

@@ -111,17 +111,22 @@ function telemetryRoute(path: string): string {
 async function parseResponse<T>(response: Response): Promise<T> {
   if (!response.ok) {
     let message = `${response.status} ${response.statusText}`;
+    let backendCode: string | undefined;
     try {
-      const payload = await response.json() as { error?: string };
+      const payload = await response.json() as { error?: string; code?: unknown };
       if (payload?.error) {
         message = payload.error;
       }
+      if (typeof payload?.code === 'string' && /^[a-z][a-z0-9_]{0,63}$/u.test(payload.code)) {
+        backendCode = payload.code;
+      }
     } catch {
       // ignore body parse failure
     }
     throw normalizeAppError(new Error(message), {
       source: 'browser-fallback',
       status: response.status,
+      ...(backendCode ? { backendCode } : {}),
     });
   }